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(NEXSTAR) – At a press conference Monday, President Joe Biden said he believes anyone who wants a vaccine will be able to get one by this spring.

“I think it will be this spring,” he said. “But it’s going to be a logistical challenge that exceeds anything we’ve ever tried in this country.”

He said he feels “confident” that by summer, “we’ll be on our way toward heading toward herd immunity and increasing access for people who aren’t first on the list, all the way going down to children.”

“I feel good about where we’re going and I think we can get it done,” he added.

Time, he acknowledged, “is of the essence” in getting the 328 million residents of the U.S. vaccinated.

Yet Biden said he is “optimistic that we will have enough vaccines.”

Going into office, he said he was unaware how much of the vaccine was available, but that information he now possesses.

He also said that he’s gotten “commitments from some of the producers that they will produce more vaccines in a relatively short period of time.”

Biden said he was confident “that we will be in a position within the next three weeks or so to be vaccinating people at the range of a million a day or in excess of that.”

As part of his COVID-19 plan, Biden has said he intends to vaccinate 100 million people in his first 100 days of office.

As of Sunday, the U.S. had administered 21.85 million doses of the COVID-19 vaccine, according to CDC data.